Interpreting Form and Symmetry in Outflows from Geriatric Stars

Hubble images of post-AGB stars in the early stages of their
mass loss are providing high-resolution (~100 AU) insights and constraints on
their highly structured mass loss mechanisms. Multi-epoch HST images are
helping to probe the growth patterns of these objects. (We shall briefly
consider a few especially well-observed cases.) However, this
talk looks beyond the images to physics of the poutflows and what they suggest
about the underlying and poorly understood ejection mechanisms Our hydro
models are revealing interpretive insights into the nature of the collimated
flow patterns seen in the images above. The nature of the mass ejection
mechanisms and their collimation are now far better constrained, almost to the
point of undermining the various ejection scenarios.